Automated manufacturing processes often require precise machining or manufacturing operations to be performed by at least one machine on a workpiece. For example, automated industrial machines may be required to initially bore one or more holes in a piece of stock material. The same machine or a second machine may then be operative to chamfer or enlarge the entrance to the previously bored hole. Still another machine or another part of the original machine may then be operative to tap threads into at least a portion of the previously bored hole. Continuing with this example, the axis of the hole being bored and tapped may be obliquely aligned to adjacent surfaces of the stock material, and at least portions of the machining operation may take place at a relatively inaccessible location within the stock material. Machining operations of this type are carried out widely, for example, in the automotive industry. Large numbers of machining operations must be carried out on engine blocks and on the housings for carburetors, fuel pumps, distributors and such. A very high degree of precision generally is required for such machining operations. This great precision not only improves the quality of the part being produced, but also increases tool life and reduces down time for a machine line. Even small improvements in the currently employed automated machine lines and corresponding reductions in down time can result in very significant cost savings.
All automated machine tool equipment includes means for adjusting the relative alignment between the machine tool and the workpiece. Some manufacturing lines may be adapted to adjust the position and alignment of the machine, others enable adjustments to the position and alignment of the workpiece, while still others enable adjustments to be effected on both the machine tool and the workpiece. The particular arrangement for adjustability will depend, in part, upon the manner of movement of the machine tool and/or the workpiece during a machining operation. Typically adjustments to the machine tool and/or the workpiece are carried out by shim assemblies which are adjustably positioned between the machine tool and a base and/or between the workpiece and a base.
Machine tool alignment typically is checked by employing a master part. A master part is a precisely manufactured piece of stock material that accurately duplicates at least a portion of a specified part. The position and alignment of the machine tool and the master part can be compared, and adjustments to one or both may be effected as needed.
The most widely employed prior art apparatus for checking alignment includes mechanical or electromechanical gauges and/or instruments. The spatial positions and orientations of tools and master parts can be determined by mechanical means which may be operatively connected to electronic readouts to provide an indication of alignment errors. These mechanical or electromechanical gauges are generally complex, costly pieces of equipment that are specifically dedicated to a particular machine or a particular type of machine. Additionally, even the most sophisticated mechanical or electromechanical gauge is subject to geometric distortion in response to the effects of gravity, temperature changes or other variables.
Laser beams are known to define a substantially straight line that is dimensionally stable over a relatively long distance. Lasers have been used in combination with photosensitive targets that are operative to sense and identify the location of the center of energy of a laser beam impinging thereon. This combination of a laser emitter and a photosensitive target have proved to be extremely efficient and accurate for measuring alignment between two spaced apart objects. In particular, the laser emitter may be mounted to one object to be aligned while the photosensitive target is mounted to the other object to be aligned.
A background discussion of early work in laser alignment is presented in Laser Alignment In Industry, ASTME Technical Paper MR68-408, 1968 and in Laser Alignment-Current Uses And Applications, SME Technical Paper MR76-864, 1976.
The operative part of a photosensitive target is a small planar photocell rigidly mounted in a housing. It is often extremely difficult to ensure that the surface of the photocell in the housing of the target is disposed at the preferred target point in the machine tool or master part to be aligned. In particular, the photocell often is disposed forwardly or rearwardly of the point to be aligned or is angularly aligned thereto because of geometric constraints of the target housing, the master part or the machine tool. These errors in the mounting position would yield measurement errors that would offset the potential accuracies of the laser alignment system. These problems were overcome by U.S. Pat. No. 4,483,618 which issued to Martin R. Hamar on Nov. 20, 1984. In particular, the target of U S. Pat. No. 4,483,618 includes a mirror disposed such that a laser beam incident upon the mirror is reflected to a photocell. The photocell is disposed such that the optical distance between the reflective surface of the mirror and the photocell is equal to the distance between the reflective surface on the mirror and a point on the workpiece or tool to which alignment will be compared. These equal distances enable accurate measurements for those instances where it is inconvenient or impossible to actually place the photocell at the desired measurement point. This equidistant relationship ensures that the target of U.S. Pat. No. 4,483,618 will provide accurate readings despite any angular misalignment of the target housing on the object to be aligned. Despite these many advantages, a target manufactured in accordance with U.S. Pat. No. 4,483,618 may be geometrically well suited for one master part or machine tool, but not geometrically well suited for a different master part or machine tool. The structural requirements of these targets makes it impractical to consider adjustably mounting the photocell relative to the mirror to better accommodate geometric constraints of the particular machine system being aligned.
Another very significant laser alignment apparatus is shown in U.S. Pat. No. 4,566,202 which issued to Martin R. Hamar on Jan. 28, 1986. U.S. Pat. No. 4,566,202 shows a laser emitter which can be mounted in a spindle or chuck of a rotating tool holder. The laser emitter of U.S. Pat. No. 4,566,202 is used in combination with a photosensitive target which may be the target of the above described U.S. Pat. No. 4,483,6I8. The laser apparatus of U.S. Pat. No. 4,566,202 is used by rotating the tool holder in which the laser emitter is mounted. An improperly aligned tool holder will cause the laser beam to generate an annulus on the target mounted in the master part. The displacement and angular alignment of the laser beam can be accurately determined by readings from the target and appropriate adjustments can be made. Although this system is extremely effective, it may require the technician to perform various arithmetic calculations to determine the type and amount of misalignment and the adjustments that would be required to correct the misalignment. These arithmetic calculations may go beyond the abilities of the technician or machinist responsible for ensuring proper alignment. Microprocessors with appropriate software have been made available through Hamar Laser Instruments, Inc. to facilitate certain of these mathematical calculations. However, some technicians have encountered difficulties in working with the available microprocessors, computers and related software. Some of the difficulties have related to the need to convert error readings into actual adjustments. Other technicians have encountered difficulties as they move the available laser alignment equipment from one machine tool and work station to another on a particular manufacturing line, or as they move the laser equipment from one manufacturing line to another. In particular, a technician may have to employ different series of alignment steps and calculations depending upon the equipment being aligned. On some equipment the laser emitter is most conveniently mounted to the tool holder, while on other equipment the laser emitter is most conveniently mounted on the master part. In some instances adjustments are most conveniently made to the tool holder, while in other instances adjustments are more readily made to the master part.
Although the laser alignment equipment shown in U.S. Pat. No. 4,483,6I8 and in U.S. Pat. No. 4,566,202 are sufficiently adaptable to be used on virtually all machine tool systems, the differences in the laser set up, mathematical calculations and alignment steps have often been confusing to the typical technician.
The prior art further includes U.S. Pat. No. 4,679,940 which also issued to Martin R. Hamar. U.S. Pat. No. 4,679,940 relates to a control system for a photosensitive target for indicating incidence of the beam on the target, for shifting the electrical sensing center of the photocell to the center of the target housing and for compensating for variations in laser beam intensity.
Another problem with even the more sophisticated laser alignment systems relates to the rotational orientation of the photosensitive target and/or the laser emitter at the time each reading is made. In this regard, a typical laser alignment system requires the laser emitter and/or the photosensitive target to be positioned at each of several different rotational orientations at which readings will be taken. The preferred measurement operation includes taking readings at four rotational positions separated from one another by 90.degree. degrees, namely 12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock. To facilitate this aspect of the laser alignment, the photocell target and/or the laser emitter may be provided with four bubble levels. The technician may be required to follow a set sequence wherein the bubble levels are sequentially employed to position the photosensitive target or the laser emitter at the 12, 3, 6 and 9 o'clock positions for readings. The computerized systems that vastly simplify or eliminate the computations required by the technician typically will specify that the readings be taken in a particular order (e.g. 12, 3, 6 and 9 o'clock). If the technician inadvertently takes readings in a different order, the computer will calculate incorrect errors and identify inappropriate adjustments to be made for correcting those errors. Thus, the great precision enabled by laser alignment equipment and the computational efficiencies afforded by computers can be completely offset by the mere incorrect order of readings taken by a technician.
Error measurement and resulting computations can be further complicated even in those situations where readings are taken in the proper sequence. For example, machine tools are often disposed in close proximity to other manufacturing hardware Structures adjacent to the machine tool being aligned may prevent the laser alignment system from being rotated through the preferred range of 12, 3, 6, and 9 o'clock orientations. In particular, the wires leading from the laser emitter or the photosensitive target may prevent complete rotation of one or both units. Although an ability to take readings at rotational positions of 2, 6 and 10 o'clock could provide the necessary data for accurately calculating errors and identifying necessary corrections, the computer may not be structured for such angular orientations and the bubble levels generally would be improperly positioned for assuring to the computer that the proper rotational orientation has been achieved.
Still further, a good quality bubble level can provide fairly accurate information as to angular orientation. However, the errors possible with a technician manually aligning a bubble level are far greater than the precision enabled by the laser emitter and photosensitive target. Thus, the high degree of precision enabled by sophisticated photo optical electronic equipment is partly offset by the inaccuracies of manually positioning a bubble level.
Although the above described laser alignment systems are extremely effective and accurate, it is desirable to provide an improved laser alignment system that can be more readily employed and understood by field technicians.
Accordingly, it is an object of the subject invention to provide an improved laser alignment system for aligning machine tools and other apparatus having parts that are movable relative to one another.
It is another object of the subject invention to provide a laser alignment system that avoids the need for mathematical calculations by the technician using the system.
It is a further object of the subject invention to provide a laser alignment system that can be used with any of a plurality of different machine tools in an industrial work place.
Yet another object of the subject invention is to provide a laser alignment system that accurately identified displacement and angular alignment errors and that further identifies the specific machine or workpiece adjustments needed to correct the errors.